test.rb

require 'rubygems'
require 'benchmark'
require 'nokogiri'

TIMES = 50_000

doc  = Nokogiri::XML(File.new("test.xml"))
node = doc.at_xpath("./strategies")

Benchmark.bmbm do |x|
  x.report("xpath/first()") do
    TIMES.times { e = node.at_xpath("./strategy[1]") }
  end
  x.report("xpath.first") do
    TIMES.times { e = node.xpath("./strategy").first }
  end
  x.report("at") do
    TIMES.times { e = node.at("strategy") }
  end
  x.report("at_xpath") do
    TIMES.times { e = node.at_xpath("./strategy") }
  end
  x.report("children.second") do # first returns a Node::Text
    TIMES.times { e = node.children[1] }
  end
end

__END__

$ ruby test.rb 
Rehearsal ---------------------------------------------------
xpath/first()     3.290000   0.030000   3.320000 (  3.321197)
xpath.first       3.360000   0.010000   3.370000 (  3.381171)
at                4.540000   0.020000   4.560000 (  4.564249)
at_xpath          3.420000   0.010000   3.430000 (  3.430933)
children.second   0.220000   0.010000   0.230000 (  0.233090)
----------------------------------------- total: 14.910000sec

                      user     system      total        real
xpath/first()     3.280000   0.000000   3.280000 (  3.288647)
xpath.first       3.350000   0.020000   3.370000 (  3.374778)
at                4.530000   0.040000   4.570000 (  4.580512)
at_xpath          3.410000   0.010000   3.420000 (  3.421551)
children.second   0.220000   0.010000   0.230000 (  0.226846)

text.xml

<strategies type="array">
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
  <strategy>
    <name>string</name>
    <path>string</path>
  </strategy>
</strategies>